These files are part of the dataset "Historical settlement composite layer for the U.S. 1810 - 2015,"
contained in the dataverse �HISDAC-US: Historical Settlement Data Compilation for the United States� 
(https://dataverse.harvard.edu/dataverse/hisdacus).

Reference:
Leyk, Stefan; Uhl, Johannes H., 2018, "Historical settlement composite layer for the U.S. 1810 - 2015,"
https://doi.org/10.7910/DVN/PKJ90M, Harvard Dataverse

Related Publication:
Leyk, Stefan; Uhl, Johannes H., 2018, "HISDAC-US: Historical Settlement Data Compilation for the Conterminous United States Over 200 Years," Scientific Data 5:180175
https://doi.org/10.1038/sdata.2018.175

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Corrigendum:

The spatial reference system used to project the layers was incorrectly described in version 1.0. This has been corrected in this new version (see below).
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This dataset contains the following files:

- FBUY.tar.gz: Archive that contains the FBUY raster composite (a value of 1 indicates the presence of built structures without built-year record only)
- FBUY_IPU.tar.gz: Contains the IPU raster layer accompanying FBUY
- FBUY_OPU.tar.gz: Contains the OPU raster layer accompanying FBUY
- FBUY_OPPU.tar.gz: Contains the OPPU raster layer accompanying FBUY

Abbreviations and explanations:
FBUY:		First built-up year. A raster composite with each pixel value indicating the year of first settlement within the pixel area.
IPU:		Inside positional uncertainty. A relative positional uncertainty measure describing the likelihood of a record located within the pixel area to be outside.
		Based on the records indicating the presence of built-up structures in the year of first settlement.
OPU:		Outside positional uncertainty. A relative positional uncertainty measure describing the likelihood of a record located outside the pixel area to be inside.
		Based on the records indicating the presence of built-up structures in the year of first settlement.
OPPU:		Overall positional uncertainty. Per-pixel average of IPU and OPU.

Data source: Zillow Transaction and Assessment Dataset (ZTRAX) (c) Zillow Inc.
Spatial resolution: 250m
Coordinate reference system:
USA Contiguous Albers Equal Area Conic USGS version (SR-ORG:7480)
https://spatialreference.org/ref/sr-org/usa_contiguous_albers_equal_area_conic_usgs_version-2/
Proj4: +proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23.0 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

Contact:
Stefan Leyk
Department of Geography
University of Colorado Boulder
GUGG 110, 260 UCB 
Boulder, CO 80309-0260, United States of America
stefan.leyk@colorado.edu